Advances in I TER relevant NbTi and Nb Sn strands and low-loss NbTi - - PowerPoint PPT Presentation

Bochvar Institute of Bochvar Institute of Inorganic Materials Inorganic Materials

Advances in I TER relevant NbTi and Nb Sn strands and low-loss NbTi Nb3Sn strands and low-loss NbTi strands in RF.

A.Shikov, V.Pantsyrny, A.Vorobieva, L.Potanina, V.Drobyshev, N.Kozlenkova, E.Dergunova, I.Gubkin, S.Sudyev.

Bochvar Research Institute of Inorganic Materials (VNIINM), Rogova St. 5, 123060 Moscow, Russia

May 21, 2008 WAMSDO 2008, CERN 1

NbTi strands for different applications

a) for MRI tomographs a) for MRI tomographs b) for AC electro technical devices c) for cryomotors

СКНТ-8910-042 Strand for accelerator UNK,

produced in amount of more than 100 tons

Strand diameter – 0.85 mm Filaments diameter – 6 µm

Jc (5T) - 2500 A/mm2

May 21, 2008 WAMSDO 2008, CERN 2

Jc (5T) - 2500 A/mm2

In the framework of ITER Project the RF Party has manufactured the NbTi Cable (~0.5 ton), and shipped it to EFDA for further fabrication of PFCI. The testing of

NbTi strands for ITER Project

Wire diameter – 0.73 mm

( 0.5 ton), and shipped it to EFDA for further fabrication of PFCI. The testing of PFCI planned to be carried out in Japan in CSMC in June 2008.

Number of filaments – 2346 Filament diameter – 9.8 mcm Cu/non Cu Ratio 1 4 Cu/non Cu Ratio - 1.4 Jc > 2700 A/ mm2 (5T, 4.2K)

(2800-2900 A/ mm2 – measured values)

May 21, 2008 WAMSDO 2008, CERN 3

NbTi strands for ITER Project RF has to produce 40 t of b i d f 1&6 NbTi strands for PF 1&6 conductors and fabricate PF1 coil

Strand PF1,6 Diameter, mm

0.73

,

0.73

Cu/nonCu Ratio

1.6

Filament diameter, µm

6.8

Filament 4314 Filament Number 4314

Extruded rod of PF1&6 experimental NbTi strand

May 21, 2008 WAMSDO 2008, CERN 4

Diameter of the billet 200 mm

ITER type strands with Cu/non Cu ratios in the wide range of 1.6 to 6.9 (ITER PF conductors) produced from the same trimetal NbTi/Nb/C bill t ith C / C ti f 0 43 NbTi/Nb/Cu billets with Cu/non Cu ratio of 0.43

PF1&6 Cu/non Cu = 1.6 PF5 Cu/non Cu = 4.4 PF2,3&4 Cu/non Cu = 6.9 ff Nb diffusion barrier is necessary for avoiding the formation of brittle inclusions of Cu-Ti i lli d

May 21, 2008 WAMSDO 2008, CERN 5

All Cu elements had RRR> 200 intermetallic compounds

Filament Distortions on the Boundary Between Filament Zone and a Bulk Cu

Strands with Cu/non Cu 1.6 met the requirements of ITER Specification for 4.2 K, 5T (Jc=2900A/mm2) Jc (4.2 K, 5 T) = 2850-2900A/mm2 “n” in the range of 50-60 Jc (4.2 K, 5 T) = 2500-2600A/mm2 “n” in the range of 25-35

May 21, 2008 WAMSDO 2008, CERN 6

ITER PF NbTi strands

150 200 250

t density )

#1 #2 #1 V

B 6 T

50 100 150

ritical current (A/mm

2)

#1 V #2 V CEA

B = 6 T

6.1 6.2 6.3 6.4 6.5 6.6 6.7

Temperature (K)

Cr

Strands with Cu/non Cu 1.6 met the requirements of ITER Specification for 4.2 K, 5T (Jc = 2900 A/mm2) 4.2 K, 5T (Jc 2900 A/mm ) At high temperature (6.5 K) and in the field of 6 T Jc < 100 A/mm2

May 21, 2008 WAMSDO 2008, CERN 7

Low-loss NbTi strands

Requirements for low-loss NbTi strands. Strands - with small diameter filaments embedded in a resistive matrix and i ti b i resistive barriers. Minimum specification for JC at 4.2 K and 5 T is 2500 A/mm2, target value for for JC at 4.2 K and 5 T is 2750 A/mm2; Filament diameter reduction with negligible coupling Maximum effective Filament diameter reduction with negligible coupling. Maximum effective filament diameter Deff is 3 µm, with a target Deff of 2 µm. The relevant value for the specification is the hysteresis loss Qh. An effective filament diameter of 3 µm corresponds to a Qh of 65 mJ/cm3 An effective filament diameter of 3 µm corresponds to a Qh of 65 mJ/cm

• f Nb-Ti for a bipolar field cycle +/- 3 T.

An effective filament diameter of 2 µm corresponds to a Qh of 48 mJ/cm3

• f Nb-Ti for a bipolar field cycle +/- 3 T;

p y ;

May 21, 2008 WAMSDO 2008, CERN 8

R&D Targets for Low-Loss Nb-Ti Strands and Cables for Fast Cycled Superconducting Magnets at CERN (L.Bottura)

Survey of hysteresis loss and Jc in various Nb-Ti strands produced in the past 10 years. The data has been

• btained from the references indicated in the legend. The rectangles represent the minimum specified

May 21, 2008 WAMSDO 2008, CERN 9

performance (solid line) and the target performance (dashed line) of Nb-Ti strands suitable for fast cycled superconducting magnets.

NbTi fine filaments strands designs (INTAS-GSI Project)

Ordinary hot double stacking (200-300 x85) single stacking of (20000) Ordinary hot double stacking (200-300 x85) g g ( ) I – hot single stacking + II-cold bonding (3000 x7)

May 21, 2008 WAMSDO 2008, CERN 10

Ordinary hot double stacking (200-300 x85)

0.825 mm strand with filament diameter of 3.5 µm: Ic = 553 A (5 T; 4.2 K); Cu/Sc = 1.415; Jc > 2500 A/мм2 n = 56; RRR 293/10 = 160 0.46 mm strand with filament diameter of 1.9 µm: Ic = 178 A (5 T; 4.2 K); Jc = 2400 A/mm2 n = 37 RRR 293K/ 10 K= 110 Resistive alloy Cu-0.5%Mn y (Annealed (500°C) RT resistivity – 3.41-3.42 µΩ µΩ-cm Resistivity in liquid helium – 1.70 µΩ-cm

May 21, 2008 WAMSDO 2008, CERN 11

es st ty qu d e u 0 µ c

Fine filament (3.5 µm in dia) NbTi 0.65 mm wire for operating in fields with sweep rate

NbTi fine filaments strands – design and properties

Fine filament (3.5 µm in dia) NbTi 0.65 mm wire for operating in fields with sweep rate up to 4 T/s, was developed in BI. The wire was fabricated by a single stacking method. Each of 10644 filaments was surrounded by a matrix of commercial MN-5 alloy (Cu- 5wt.%Ni). The spacing is 0.5 µm. Cu/non Cu = 1.8. The central Cu core, tubes and the external sheath are fabricated from Cu with (R273/R10) > 250. RRR of the strand ∼200. external sheath are fabricated from Cu with (R /R ) > 250. RRR of the strand 200. Jc ≥ 2900 A/mm2 (5T 4 2K) The hysteresis losses = 51 kJ/m3 per wire and 144 kJ/m3

May 21, 2008 WAMSDO 2008, CERN 12

Jc ≥ 2900 A/mm (5T, 4.2K). The hysteresis losses 51 kJ/m per wire and 144 kJ/m per SC volume.

NbTi strands in resistive matrix for nuclotron type cable designed for application in fast rate changing (up to 4T/s) magnetic field

The design of trapezoidal cross section NbTi/Nb/C 5%Ni/C i ith 10374 fil t NbTi/Nb/Cu-5%Ni/Cu wire with 10374 filaments (6µm) fabricated by single stacking from billet 150 mm in dia. Cu/non Cu ratio= 1.8. NbTi, Nb, CuNi and Cu occupy 33.3; 2.7; 18.5 and 45.5

May 21, 2008 WAMSDO 2008, CERN 13

Cu a d Cu occupy 33 3; ; 8 5 a d 5 5 percent of a the strand’s cross section area. cable of SIS100 type

3000

Properties of the trapezoidal cross section NbTi/Nb/Cu-5%Ni/Cu wire

2000 2500 3000 t Density,

2

B=1.05 T 30 40 50 cm

3 cycle

500 1000 1500 Critical Current A/mm

2

B=0.54 T 10 20 Losses, mJ/c

5 7 9 11 13 Twist Pitch, mm

Specified Jc(5 T) 5 T, Sample 6 T, Sample 7 T, Sample 8 T, Sample 5 T, Batch 6 T, Batch

1 2 3 4 5 6 7 Field ramp rate, T/s

The dependences of Jc at fields of 5,6,7 and 8 T on twist pitch for the samples (hollow marks) J > The AC losses were measured by calorimetric method at field amplitudes B=1.05T and B=0.54T. At nominal for SIS 100 dipole field rate of 4 T/s and samples (hollow marks). Jc > 2700 A/mm2 at 5 T until twist pitch is more than 10 mm (∼3πd). SIS 100 dipole field rate of 4 T/s and field amplitude B=1.05 T the losses value normalized to

• verall

wire volume is less than 30 mJ/cm3 and

May 21, 2008 WAMSDO 2008, CERN 14

80 for NbTi.

Starting from the middle of 1970-s both main types of Nb3Sn multifilamentary

ITER type Nb3Sn strands

Starting from the middle of 1970-s both main types of Nb3Sn multifilamentary strands (bronze and internal tin) were under the development. 650 filaments 361 filaments

May 21, 2008 WAMSDO 2008, CERN 15

Cu stabilized Internal tin strand Non stabilized bronze processed strand

Strand diameter – 1.5 mm

Non stabilized Nb3Sn strand for Tokamak T-15

Number of filaments – 14641; Filaments diameter - 5 µm; Jc (8 T)- 510 A/mm2 Ic (average) –900 A Th i i l f T 1 d The critical current of T-15 conductor was ~ 11.5 kA in a field of 8 Т or ~ 110% of single strands current ability (900A x 11). Approximately 90 tons of conductor were produced in an industrial way, which assumed production of more than 25

May 21, 2008 WAMSDO 2008, CERN 16

tons of strands.

Nb3Sn strand for model TFCI (ITER Model coils program)

(Designed and produced in amount of 1 ton)

Requirements:

Jc (12T) > 550 A/mm2 Jc (12T) > 550 A/mm2 Hysteresis losses (+/-3T) < 200 mJ/cm3 RRR > 100 Diameter = 0.81mm Cu/(non Cu) = 1.5

May 21, 2008 WAMSDO 2008, CERN 17

In collaboration of VNIINM, VNIIKP and NIIEFA the TFCI has been produced as a part of ITER Model Coils Program

The coil reached the designed parameters: Current – 46 kA at Magnetic field – 13 T

May 21, 2008 WAMSDO 2008, CERN 18

The effect of degradation under mechanical loading was identified as an important issue for large magnet systems wound

Tensile testing of bronze processed Nb3Sn strand 1 5 mm in dia

identified as an important issue for large magnet systems wound with CICC on the Stage of ITER Large Model Coils Program

Tensile testing of bronze processed Nb3Sn strand 1.5 mm in dia with 14641 filaments

0% 1%

May 21, 2008 WAMSDO 2008, CERN 19

Nb3Sn strands with enhanced mechanical strength

Cu-Nb alloy Mechanical strength was significantly (in a

High strength wire

g g y ( factor of 1.3-1.5) increased by replacing of part of stabilizing Cu on the nanostructured Cu-Nb layer. Jc of reinforced strands maintains at the same

Reference wire

May 21, 2008 WAMSDO 2008, CERN 20

reinforced strands maintains at the same level.

Nb Nb3Sn internal Sn internal-

• tin strand for

tin strand for ITER TF conductor sample ITER TF conductor sample test tested ed in SULTAN in SULTAN

Development and Development and fabrication of Nb fabrication of Nb3Sn internal Sn internal-

• tin strand, meeting ITER TF specification for

tin strand, meeting ITER TF specification for TF conductor TF conductor’s ’s Cross-sections of internal-tin strand 0.82 mm in dia: a – before reaction heat treatment; SULTAN sample testing SULTAN sample testing. F . Fabricated abricated strand t strand total

• tal amount

amount -

• 11

10 0 kg kg (22,5 (22,5 km km) ) f ; b – after reaction heat treatment;

a b

Parameters and properties ITER TF strand specification Experimental results Outer diameter of the strand, mm

0.82±0.003 0.82±0.003

Cu:non-Cu ratio 1.0 ±0.05 0.996 ±0.03 Fil t b 2947 Filament number

• 2947

Barrier material

• Ta

Non-Cu critical current density (at 12 T, 4.2 K, 0.1 µV/cm)

> 800 A/mm2 830-950 A/mm2

Non-Cu hysteresis losses < 1000 kJ/m3 850 980 kJ/m3

Conductor Cabling Layout [Option 1] ((2+1Cu)×3×5×5+core)×6 (Produced by VNIIKP)

T > 6K

May 21, 2008 WAMSDO 2008, CERN 21

y

• n ±3T field cycle at 4.2 K

< 1000 kJ/m3 850-980 kJ/m3 RRR 4.2 K > 100 102-110 “n”-value > 20 30-45

Tcs > 6K

ITER type High Jc type

Nb Nb3Sn internal Sn internal-

• tin strands

tin strands

ITER type High Jc type Jnc, non-Cu critical current density [A/mm2] @12 T, 4.2 K, 0.1 µV/cm, no external strain

745 2070

C l l d l f i f Nb S i id

38 9

Calculated volume fraction of Nb3Sn inside diffusion barrier, %

38.9 45.8

Wh, Hysteresis Loss [mJ/cm3 non-Cu], @± 3T ~300 >1000 Calculated Jc( Nb3Sn) [A/ mm2] @12 T, 4.2 K

2180 4850 The quality of Nb Sn phase after heat treatment with last stage at 5750C 150h The quality of Nb3Sn phase after heat treatment with last stage at 5750C 150h + 6500C 200h is essentially close to a quality observed in bronze processed strands (uniaxed grains and average grain size - approximately 90 nm). The analysis of microstructure enables to suggest that large increase of Jc (not proportional to the increase of volume fraction of Nb3Sn phase) is probably caused by the bridging of filaments. At the same time too strong bridging is negative for stability of the wires.

May 21, 2008 WAMSDO 2008, CERN 22

bridging is negative for stability of the wires.

Perspectives of upgrading of bronze processed Nb3Sn strands The practically attainable volume fraction of Nb3Sn phase in bronze process strand is ∼ 35% in the area inside the diffusion barrier process strand is 35% in the area inside the diffusion barrier Therefore the requirement of Jnc = 800 A/mm2 (standard 12 T, 4.2K) assumes the attaining of critical current density in Nb3Sn phase approximately 2700 A/mm2 approximately 2700 A/mm2. Three main possible ways of Jc increase could be considered:

• increase of quantity of Nb3Sn phase (equal to increase of Sn in bronze

increase of quantity of Nb3Sn phase (equal to increase of Sn in bronze matrix)

• increase of quality of Nb3Sn phase (increase of pinning by modification of

microstructure) microstructure)

• controlled bridging (optimization of the strand’s design)

May 21, 2008 WAMSDO 2008, CERN 23

Increasing of tin content in Cu-Sn bronze

As cast As cast

α (α+δ) (α+δ)

Cu31Sn8

Homogenized

May 21, 2008 WAMSDO 2008, CERN 24

In the Cu-Sn matrix alloys the Sn content gradually increased from 10wt% up to 16wt%

The artificial doping of the Nb filaments by

Enhancement of Nb3Sn strands properties

The artificial doping of the Nb filaments by Ti has been designed and proved to be effective for both types of Nb3Sn strands (bronze processed and internal tin) (bronze processed and internal tin)

May 21, 2008 WAMSDO 2008, CERN 25

Microstructure of Nb Sn Enhancement of Nb3Sn strands properties Microstructure of Nb3Sn layers with the use of artificially Ti doped Nb filaments (introduction of

new sources of pinning)

May 21, 2008 WAMSDO 2008, CERN 26

Bronze processed Nb

Nb3Sn Sn strands

Enhancement of Nb3Sn strands properties p

3

(with controlled bridging of filaments) Diameter of filaments ∼ 2.5 µm Bronze matrix alloy – Cu-14wt.%Sn

Qh (±3T) = 546 kJ/m3 Qh (±3T) = 786 kJ/m3

May 21, 2008 WAMSDO 2008, CERN 27

y Jc (12 T, 4.2 K, 0.1 µV/cm) > 750 A/mm2

Bronze processed Nb

Nb3Sn Sn strands

1000 12684 fil

Bronze Nb3Sn strand could be produced with Jc (12T) up to 800–900 A/mm2

800 900 , 4.2K) 12684 fil 7851 fil 7225 fil 700 800 Cu (12T, 500 600 Jc non 400 0,5 1,5 2,5 3,5 4,5 Diameter of filaments mcm

May 21, 2008 WAMSDO 2008, CERN 28

Diameter of filaments, mcm

Cross-section of advanced ITER strand (0.82 mm)

(To be produced in amount of 80 tons for ITER TF Conductor) Ta Ta Cu Cu ( p ) Bronze Cu Bronze Cu-

• (14

(14-

• 14.3)%Sn

14.3)%Sn Nb Nb Nb Nb3Sn filaments Sn filaments

May 21, 2008 WAMSDO 2008, CERN 29

Advanced ITER strand for TF conductor

Hysteresis Loss, mJ/cm3 300-350 Jc (12T, 4.2K), A/mm2 900 «n» > 30

400

2100 2300 2500

8T

300

1500 1700 1900

c, А/mm2

10T

100 200

900 1100 1300

Jc

10T 12T

20 40 60 80 100 120 140

700 0,4 0,6 0,8 1

Diameter of the strand, mm

May 21, 2008 WAMSDO 2008, CERN 30

Nb3Sn and NbTi strands with enhanced heat capacity

Material Heat capacity at 4 -6 К, Thermal conductivity at 4 - 9 Density Melting Material Heat capacity at 4 6 К, J/(cm3 *K) Thermal conductivity at 4 9 K (mW/cm*K) Density at RT, (g/cm3) Melting temperature,

оC

Cu 0.002 6000 8.94 1085 Nb Sn 0 008 3 ~8 9 Nb3Sn 0.008 3 ~8.9 NbTi ∼ 0.002 1.5 6.1 ~1920 CeCu 0 033 10 8 262 ~875 CeCu6 0.033 ∼10 8.262 ~875 HoCu2 0.300

• 9.147

~900 PrB6 0.2-0.15 ∼80 4.85 ∼2500 Ce(Al0 9Cu0 1)2 0.064 ~10 4.93 ∼1460 Ce(Al0.9Cu0.1)2 0.064 10 4.93 1460 Gd2O2S 0.660 ∼50 7.44 >1500

The traditional stabilization method of adding copper to the conductor cross section The traditional stabilization method of adding copper to the conductor cross section reduces the overall critical current density. Another approach to the stability increase - doping with some extremely large specific heat capacities substances at low temperature.

May 21, 2008 WAMSDO 2008, CERN 31

1

Nb3Sn and NbTi strands with enhanced heat capacity

2 Cu ∅4 ∅13

NbTi filaments

5 PrB6 ∅0.8

0.73 mm NbTi samples with/without Gd2O2S doping

mm Nb tube Cu Ta barrier

May 21, 2008 WAMSDO 2008, CERN 32

0.82 mm Nb3Sn samples with/without PrB6 doping

Nb3Sn and NbTi strands with enhanced heat capacity

rgy, J gy, J ritical ener ritical energ Transport current, A Transport current, A C Cr

Critical energy versus transport current for 0.73 mm NbTi samples with/without Gd2O2S doping Critical energy versus transport current for 0.82 mm Nb3Sn samples with/without PrB6 doping

May 21, 2008 WAMSDO 2008, CERN 33

6

p g

summary summary

• NbTi strands with Cu/non Cu ratio 1.4-1.6 designed for the use in

ITER PF 1&6 coils have Jc ≥ 2900 A/mm2 (5 T, 4.2 K). Increase of C / C ti t 6 9 i ITER t NbTi t d d i d f th Cu/non Cu ratio up to 6.9 in ITER type NbTi strands designed for the use in ITER PF 2-5 coils led to 10% drop in Jc values.

• NbTi strands with low-loss for application in Fast Cycled

Superconducting Magnets made a good progress recently (strands with 3-4 µm filaments in resistive matrixes have been produced), the work is in progress. Still some R&D work has to be done to attain t t l target value.

• Bronze processed ITER type Nb3Sn strands have made a good

progress in critical current density, attaining 800 A/mm2 (non-Cu, 12T, p g y, g ( , , 4.2K) in commercially produced wires. In laboratory scaled wires 900 A/mm2 (non-Cu, 12T, 4.2K) has been attained.

May 21, 2008 WAMSDO 2008, CERN 34